House Speaker Thomas P. (Tip) O'Neill (D-Mass.) has sent the White House a message about this summer's battle over a housing subsidy bill--one that actually may be saying more about this fall's political wars.

Citing a string of dismal statistics on homebuilding this year, O'Neill told Office of Management and Budget Director David A. Stockman that the government "needs to act and act now to relieve the historical depression in the housing industry."

Stockman sent House and Senate Republican leaders a letter earlier this week calling Congress' $3 billion housing subsidy plan "particularly unacceptable" and saying there is "no justification for expanding the federal role in this area."

President Reagan has threatened to veto any housing "bailout" plan as too costly and as setting a bad precedent for other beleaguered industries. Stockman's letter seemed merely to confirm that the president would not change his mind and sign a conference compromise reached last week.

If Reagan does veto the measure--being billed as a jobs program and the one piece of antirecession legislation passed this year--the Democrats think they have a good political issue to exploit this fall, House and Senate staff aides say.

In his response to Stockman, O'Neill envisioned large-scale shut-downs of small builders if something is not done to relieve their plight soon. "These small builders are staying in business today based on the hope there will be some kind of recovery. Unless they get good news now, many will disband their crews, sell their equipment and close down," O'Neill said.

The plan calls for the federal government to pay 4 percentage points of the mortgage interest rate for some moderate-income buyers of new homes. The legislation moved with remarkable speed through the House and Senate, getting more than two-thirds majorities in both houses. It is attached to a supplemental appropriations bill nearing final action in Congress once an unrelated amendment on senators' outside income is resolved.

Meanwhile, Sen. Richard Lugar (R-Ind.), the author of the original bill, still is hoping to convince the president to sign the bill when it gets to his desk. He also wrote a response to the Stockman letter, objecting to the charge that the program is a "bail-out" that would produce negligible new jobs and houses.

If Reagan does veto the bill, House and Senate Republicans will have a hard choice to make. House Republicans fell in line behind the president in a procedural vote aimed at removing the housing program from the appropriations bill on Wednesday. But a veto override would provide a more clear-cut and visible vote on policy, analysts point out.

This would make opposing the president more difficult for Republicans on the one hand--and voting down Congress' one antirecession bill more difficult on the other.